(a) Field of the Invention
The present invention relates to a method for establishing anchorage stanchions for horizontal lifelines to be supported from rebar extending from the tops of poured in place concrete columns. Additionally this invention relates to a method for clamping, to various sized rebar, the tie back cables used to anchor the stanchions. Still further, this invention relates to a method for the rigging of horizontal lifeline rebar stanchion assemblies that will allow the lifelines to be arranged in a square grid for overall access to the area that the horizontal lifelines circumscribe. Additionally this patent relates to a method to terminate horizontal lifeline cable ends and improve ease of line length adjustment and pre-tensioning.
(b) Discussion of Known Art
Stanchion systems are currently used in many applications for horizontal lifeline anchorages. These systems typically bolt or weld to I-beams or other clamped structures. When stanchions must be erected on concrete floors or columns the large flat areas do not provide surfaces that can be readily attached to. Some users have tried inserting concrete anchor bolts into drilled holes for this purpose but found that the loads required often exceed the maximum capacity of the concrete anchor bolts. Only attachment to something deeply inset into the concrete would provide the necessary strength. Thus, the embedded rebar became the obvious choice for anchorage attachment.
The United States Occupational Safety and Health Administration (OSHA) requires that horizontal lifeline systems be rigged so that freefall cannot exceed 6 ft. When working on a deck or any elevation in which no overhead anchorage locations exist tying off at ones feet with a 6 ft. lanyard would create a 12 ft. freefall. The use of stanchions that tie back into the deck or column structure enable overhead anchorage points or lines to be established. So long as the elevation of the stanchion is at least the same elevation as that of the dorsal D-ring of the workers harness, the freefall will be limited to 6 ft. This present invention relates to a method for erecting a stanchion over a rebar and then tying the top of the stanchion back to other rebar in the same column using a rebar clamp that increases its clamping force as the force that is applied to it increases. This stanchion can also be configured to use twin heads that allow lifelines to be run at right angles to each other from the same stanchion. With this configuration one can create a grid around a floor opening over which workers must travel to install metal decking or pour forms for construction. This allows for many workers to be working in one area at the same time. Existing methods to rig lifelines to rebar include anchorage straps around tied rebar columns or cable loops around tied rebar columns. These generally are of insufficient strength and rigidity to carry the loads since the rebar has very little stiffness in the direction of load. These methods also do not allow pre-tensioning of lifeline cable to reduce input energy. At best, exiting methods to solve the problem of horizontal lifeline installations attached to rebar columns are inadequate if not dangerous.
An example of a lifeline support that includes a stanchion can be found in U.S. Pat. No. 5,863,020, to Olson et al., incorporated herein by reference.
It has been discovered that the problems left unanswered by known art can be solved by mounting stanchions on building structure, such as concrete structure or concrete columns and elevated surfaces by supporting these stanchions on rebar stubs that are found protruding form the columns, or on studs fastened into the structure. These stanchions may be of varying heights but should be above 42 inches and preferably above 60 inches with some as high as 84 inches above the walking working surface. The stanchions may be constructed of steel, aluminum, composite fiber material or other generally rigid material, and may be round or square. An important example discussed herein is made of steel tube approximately 2.5 inches in diameter and 66 inches long with a load ring weld 6 inches down from the top of the stanchion tube. The rebar stanchions may be used in pairs to support each end of a lifeline or in quad groups to create a group of four lifelines that attach to each other in a square formation. Some stanchions may be used as end anchorages and some may be used as bypass stanchions. In another aspect this invention relates to an improved method for installing, adjusting and tensioning steel cable horizontal lifelines to improve efficiency and reduce overall installation cost, through the use of inline cable clamps to terminate the cable ends and synthetic webbing line tensioners to provide take up and pre-tensioning of the line to shorten apparent horizontal lifeline line length.
The method includes the steps of:
Providing a stanchion with an aperture that allows the stanchion to be placed over rebar stubs or studs that project from the structure;
Providing guy members and tieback clamps that can be used to anchor the stanchion to the structure; and
Tensioning the guy members to stabilize the stanchion over the rebar or stud.
Another aspect this invention relates to the method of attaching a horizontal lifeline between the rebar anchorage stanchions. In most cases the installation of horizontal lifelines is a time consuming process because the lifeline lengths must be accurately measured and constructed to control horizontal lifeline sag which determines line load amplification, the present invention provides a new method for lifeline installation which greatly reduces the time required. Typical lifelines use eyes with cable clamps, open wedge sockets, or combination clamps to terminate horizontal lifeline cable. The installation of these items creates tight bends in the horizontal lifeline cable, which leaves kinks in the cable when removed. The present invention uses an inline cable clamp, which is a flat plate-in which the helical lay of the cable has been machined. When the cable is clamped between 2 flat inline cable clamp plates, the cable is terminated without bending or kinking the cable. This may be installed quickly and it allows the cable to be moved to other applications requiring different lengths without the annoyance of having kinks or bends in the horizontal lifeline cable.
In another aspect the invention relates to an improved method for adjusting the length of a horizontal lifeline cable during installation. Most cables used in horizontal lifeline applications are adjusted for length using turnbuckles or rigging screws. These typically have take up lengths of 6 to 12 inches requiring a cable length to be accurately measured and constructed prior to installation. This is a very time consuming process although acceptable for permanently installed systems. When systems used in concrete construction must be moved rapidly as in the case of the rebar stanchion systems, a new method has been developed. This method uses nylon or polyester or other high strength synthetic fiber sling webbing reeved through anchor strap load binders to provide take-up and pre-tensioning of the horizontal lifeline. The sling webbing is typically 2 inches or 3 inches in width and typically from 15,000 lb. to 30,000 lb. in breaking strength. In its preferred embodiment this load binder anchor strap assembly allows up to 10 ft. of rapid take up in the horizontal lifeline cable allowing for much quicker horizontal lifeline cable installation. The load binders also have sufficient torque to allow the horizontal lifeline cable to be pre-tensioned from 300 lbs. to 1500 lbs. of pre-tension.
It should also be understood that while the above and other advantages and results of the present invention will become apparent to those skilled in the art from the following detailed description and accompanying drawings, showing the contemplated novel construction, combinations and elements as herein described, and more particularly defined by the appended claims, it should be clearly understood that changes in the precise embodiments of the herein disclosed invention are meant to be included within the scope of the claims, except insofar as they may be precluded by the prior art.